Optical Sensors for the Analysis of Alcohols in Fuels

This thesis reports the development of optical sensors to analyze alcohols in fuel samples. One optical sensor enables the analysis of phenol in aviation fuels and cellulosic biofuels. It is critical to monitor the concentration of phenols in fuels because they increase the presence of solid oxidative deposits and lower the thermal stability of fuels. Preliminary studies of another optical sensor have been conducted to detect ethanol in E10 gasoline samples. Gasoline containing ethanol is widely available and used, but the exact percentage of ethanol is not specified and varies between samples and regions. Higher concentrations of ethanol in gasoline can cause damage to vehicle parts and engines, especially in older vehicles. Therefore, it is desirable to develop a sensor that can quickly and easily determine the percentage of ethanol in gasoline. It is imperative for on-site, portable, inexpensive, and easy-to-use technologies for monitoring phenol and ethanol in fuel samples.

The optical sensors reported herein use a solvatochromic dye, Nile Blue Chloride, which is embedded within a polymer thin film. Many polymer thin films have been studied and are detailed in this research thesis. The polymer is dissolved in tetrahydrofuran through sonication and mixed with the dye. The polymer and dye mixture is spin-cast onto a glass substrate, resulting in an optical sensor. The solvatochromic dye in the optical sensors displays a color change upon a change in the microenvironment, including solvent polarity. Upon exposure to phenol or ethanol, the optical sensor exhibits a color change from purple to blue. This observation is due to the tetrahydrofuran molecules being replaced by phenol or ethanol molecules, thus creating a new microenvironment around the dye molecules. This change is monitored visually and with an ultraviolet-visible spectrometer to determine the concentration of phenol or ethanol.